After a vessel has been thrown, patterns may be scratched upon it with a graver ; if the clay be still moist, a ridge will be left by the tool on each side of the incision ; the ridge, however, will not be formed if the clay be already dry. If colour be afterwards applied, the ridge, when present, forms an outline to the colour. Rings may be left upon the eurface of ware by the thrower, and may be carved by the artist. Etching and carving as described are generally applied to fine stone ware. This ware may also be decorated by the following processes :—By dipping a dark ware in a light-colnured clay slip, and etching through the latter so as to disclose the dark background ; by modelling the borders of patterns out of strips of clay laid upon the vessel whilst still plastic ; by painting upon a, dark body with light-coloured clay pigments, in certain cases, using a vitrifiable pigment, so as to become semi-transparent, aud to disclose the background; by applying to the surface of ware, dots, rosettes, gems, or patterns, previously moulded in plaster moulds, or modelled ornaments in the form of dragons or face& The decoration known as pate sur pcite, and generally applied upon china or porcelain, and covered with glaze, is produced by modelling in a poreelainous paate spread upon the surface of the ware. The surface of the ware is generally of a dull-grey or green colour, applied to the ware by dipping in a coloured slip or glaze. The colour shows through the thinner parts of the sculptured ornament, the paste euiployed being of a semi-vitreous character. The bas-reliefs applied to Wedgwood's jasper ware are formed in moulds, and are made to adhere to the unbaked vvare, by means of liquid slip. The ware, if it be not already coloured in its sub dance, is generally dipped in a coloured slip, before the application of the bas-reliefs. Certain wares are decorated with flowera and delicate sprays of foliage, to the manufacture of which, refer ence has already been made.
The glaze is a simple form of applied decoration. It is, as has already been dated, a glass built up of two or more silicates. The normal felspathic glaze conaists of sodic or potassic and aluminic silicates; salt glaze, of sodic and aluminie silicates ; lead glazes are mixtures of plumbic with alutninic silicate, and small quantities of sodic and potaseic silicates. There are also glazes containing zincic silicate, and ferric ailicate, and, in some cases, one silicate is replaced by a borate. Glazes may be rendered white and opaque by the addition of an infusible excess of stannic and arsenic oxides, and may be coloured by metallic oxides, in the same manner as glasses. Glazes are applied by dipping, and by volatilization. The difficulty in preparing a glaze is the regulation of the mixture, so that the contraction of the glaze after fusion shall not be unequal to that of the body to which it is applied.
The well-known decorative effect of " crackle-glaze" is obtained by an adjusted disagreement between the body and the glaze. If the disagreement be allowed to go too far, the glaze chips
away frorn the body. The requirements of a glaze are (1) agreement with body, (2) power of redding solution and corrosion, (3) purity of colour, (4) povver of developing applied colours. The felspathic and aodic silicate glazes are the most durable; tbe plumbic eilicate glaze is liable to gradual decay, which is indicated by the appearance of a beautiful iridescent film. " Smears" and " flows" are glazes applied by volatilization. In the former process, the saggere are washed inside with a mixture of one or more nf the following substances : salt, ed-lead or litharge, potassic nitrate, potassie carbonate, and china stone. The ware, generally fine stone-ware, is expoeed in these saggers, and receives a gloss by the deposition and cornbination of the volatilized -mixture. The object of the use of "flows " is to soften or blur the outline of under-glaze painting or printing. Amrnonic chloride, alum, and chalk, together with one or more of the materials used for " smears," are placed in small biscuit-cups in the aaggers, together with the ware. The glass which is formed by the deposition of the mixture on the ware partially dissolves the colouring oxide, and softens the general effect. Plumbic silicate glazes are e.oloured by metallio oxides, and are used for colouring ware. In this way, imitation " crown " ware is often tnannfactured. A mottled or marbled surface is sometimes produced on ware by instilling differently coloured glazes from a vessel containing several chambers communicating with a composite neck. Opaque glazes or enamels are used to conceal a coloured body. Majolica is generally made of common fire clay or tnarl, and is coated with opaque white enamels, upon which, whilst still moist, coloured enamel decoration is applied. Litnoges ware is a clay body decorated by the aid of coloured enamels.
Cloissonn6 ware, the outline is marked out by metallic threads soldered to a metallic body, and the interstices are filled up with enamels. Imitation Cloissonne is produced by painting on a white clay body with coloured enamels, or by forming a raised outline by painting with a mixture of iron and copper dust, hardeoing the same by fire, and filling in with colour. Palisey ware has a white or coloured body, covered with transparent coloured glazes. Bristol ware is coloured by coloured felspathic glazes. A curious lustrous or glistening effect may be caused by applyiog eoarsc ly powdered mica to the surface of ware. Genuine lustre or iridescence is produced by the irre gularity of a glazed surface, caused either by decay, or by the adhesion of au almost imperceptible metallic film. Bismuth, gold, silver, copper, zinc, iron, and platinum are used for this purpose. The metallic salt is generally mixed with some strong reducing agent, and applied to the ware as a paint. The ware is then fired in a reducing atmosphere, the salt is reduced, and the metal is fixed upon the glaze of the ware by heat.